my ducks built a nest and laid their eggs in it..but ducks don't lay their eggs all at once, they lay one or two..then maybe the next day they'll lay another couple and then they sit on the eggs when they've gotten all their eggs laid..during this time quite often if the predators or snakes or anything else finds the nest they'll take the eggs..i fournd several broken eggs and their were still  4 left..the mother at that point had abandon the nest so i took the eggs..2 of them hatched..a 4th is going to hatch.  One of my other ducks just lays eggs all over the place..in the lake, on the edge..but she's young and inexperienced.  I've taken several of them and incubated them..one of them is almost ready to hatch..many of them weren't able to hatch because by the time i found them i had no idea how long they'd been there..some were under water and the lake is cold.  I'd say if you make a nest for them there is no guarantee they'll lay in it because they like to choose where they want their nest.  if they have success in their nest and predators don't find it then they'll go back the next year.